The present invention relates to a wafer abrasive machine, more precisely relates to a wafer abrasive machine, in which a surface of a wafer held by a holding plate is pressed onto an abrasive face of an abrasive plate and relatively moved with respect thereto so as to abrade the surface of the wafer.
An example of a conventional abrasive machine for abrading silicon wafers for semiconductor devices is shown in FIGS. 9 and 10. FIG. 9 is a partial sectional view of the conventional machine; FIG. 10 is a partial enlarged view of the machine shown in FIG. 9.
In the abrasive machine shown in FIGS. 9 and 10, an abrasive face 22 is constituted by an abrasive cloth 21 adhered on an upper face of an abrasive plate 20.
A top ring xe2x80x9cTxe2x80x9d is headed toward the abrasive face 22 and provided to a lower end of a rotary shaft 28, which is rotated by a motor 64 with gears 66 and 68. The top ring xe2x80x9cTxe2x80x9d and the rotary shaft 28 are vertically moved by a cylinder unit 56.
A through-hole 30 is formed in the rotary shaft 28, and a suction pipe 18, which is connected to a connecting port 74 communicated with a vacuum generator, runs through the through-hole 30. A space between the suction pipe 18 and an inner face of the through-hole 30 is an air path 32, which is connected to a connecting port 76 communicated with an air compressor. Therefore, compressed air, which is a pressure fluid, runs through the air path 32.
The top ring xe2x80x9cTxe2x80x9d provided to the lower end of the rotary shaft 28 includes a head member 24, which is fixed to the rotary shaft 28, and a holding plate 10, which is held and accommodated in a concave section 26 of the head member 24 and whose lower face 11 faces the abrasive face 22 of the abrasive plate 20. The lower face 11 of the holding plate 10 acts as a holding face capable of sucking and holding a silicon wafer xe2x80x9cWxe2x80x9d. A plurality of holes 12 are opened in the holding face 11 of the holding plate 10. As shown in FIG. 10, the holes 12 are mutually communicated by a horizontal connecting path 14 formed in the holding plate 10. The connecting path 14 is communicated to the suction pipe 18 via a connector 16. With this structure, the wafer xe2x80x9cWxe2x80x9d can be sucked and held on the holding face 11 of the holding plate 10 by driving the vacuum generator.
The holding plate 10, whose holding face 11 faces the abrasive face 22 of the abrasive plate 20, is suspended and accommodated in the concave section 26 of the head member 24 by a elastic sheet member 38, which is formed into a donut-shape and made of rigid rubber. A symbol xe2x80x9chxe2x80x9d stands for a length of projecting the holding plate 10 from the concave section 26.
An elastic O-ring 34, which is made of rubber or the like, is provided between an outer circumferential face 10a of the holding plate 10 accommodated in the concave section 26 and an inner circumferential face 24a of the concave section 26. The O-ring 34 contacts the both faces 10a and 24a. With this structure, the holding plate 10 can be slightly moved in the horizontal direction and capable of absorbing a horizontal functional force which is generated while the wafer xe2x80x9cWxe2x80x9d is abraded.
A ring-shaped restraint member 36, which is made of resin, e.g., acetyl resin, is fitted in the concave section 26 so as not to damage the holding plate 10. The restraint member 36 restrains the horizontal movement of the holding plate 10, which is accommodated in the concave section 26, within a prescribed range.
By the O-ring 34 and the restraint member 36, the horizontal movement of the holding plate 10 is limited, the vertical movement thereof is allowed.
An outer edge of the elastic sheet member 38, which suspends the holding plate 10 in the concave section 26, contacts an upper face of a step section 24b, which is formed along an outer edge of an inner upper face of the concave section 26, and is air-tightly fixed thereto by a fixing plate 40 and screws 42. An inner edge of the elastic sheet member 38 is air-tightly fixed to an upper face of the holding plate 10 as well. With this structure, a space 50 is formed between the elastic sheet member 38 and the inner upper face of the concave section 26. The air path 32 for introducing the compressed air is communicated to the space 50.
When the air compressor is driven and the compressed air is introduced into the space 50 via the air path 32, inner pressure of the space 50 rises. If the inner pressure is greater than elastic force of the elastic sheet member 38 which biases the holding plate 10 toward the inner upper face of the concave section 26, the lower end part of the holding plate is further projected from the concave section 26 as shown in FIG. 11. A symbol xe2x80x9chxe2x80x9d shown in FIG. 11 stands for the length of projecting the holding plate 10, which has been further projected by the compressed air. Of course, the length xe2x80x9chxe2x80x9d is longer than the length xe2x80x9chxe2x80x9d (see FIG. 10).
In the case of abrading the wafer xe2x80x9cWxe2x80x9d by the abrasive machine shown in FIGS. 9 and 10, the wafer xe2x80x9cWxe2x80x9d is sucked and held on the holding face 11 of the holding plate 10, and a bottom surface of the wafer xe2x80x9cWxe2x80x9d is headed toward the abrasive face 22 of the abrasive plate 20. Then the wafer xe2x80x9cWxe2x80x9d and the abrasive plate 20 are relatively moved so as to abrade the bottom surface of the wafer xe2x80x9cWxe2x80x9d. While the abrasion, a pressing force of the cylinder unit 56 and the inner pressure of the space 50 are adjusted so as to press the bottom surface of the wafer xe2x80x9cWxe2x80x9d onto the abrasive face 22 of the abrasive plate 20 with proper force.
To easily control the length of projecting the holding plate 10 from the concave section 26 of the head member 24, the elastic sheet member 38 made of soft rubber was used instead of that made of the rigid rubber. In this case, the elastic sheet member 38 was excessively extended despite the inner pressure of the space 50 was slightly risen. To properly extend the elastic sheet member 38 when an external force is applied, the elastic sheet member 38 is reinforced by a cloth-formed reinforcing member 41 as shown in FIG. 12A.
The cloth-formed reinforcing member 41 is shown in FIG. 12B. When external forces F1 are applied to warps 41a and woofs 41b in parallel, the reinforcing member 41 is less deformed. On the other hand, when external forces F2 are diagonally applied to the warps 41a and woofs 41b, the reinforcing member 41 is fairly deformed. Degree of extension of the cloth-formed reinforcing member 41 is varied by the direction of the external force.
Since the holding plate 10 is suspended by the elastic sheet member 38 whose degree of extension is varied by the direction of the external force, the movement of the holding plate 10 is varied by the direction of the external force applied while the holding plate 10 is rotated. By the variation of the movement of the holding plate 10, a gravity center of the wafer xe2x80x9cWxe2x80x9d, which is held and pressed by the holding plate 10, is shifted from a rotational axis thereof, so that an edge of the wafer xe2x80x9cWxe2x80x9d is apt to be abraded diagonally.
If density of fibers, i.e., warps and woofs, of the reinforcing member 41 is made higher, the variation of the deformation of the elastic sheet member 38, which depends on the direction of the external force, can be made small, but the problem caused by the variation still exists. Further, the reinforcing member 41 whose density of fibers is high is apt to peel from the rubber constituting the elastic sheet member 38.
In the top ring xe2x80x9cTxe2x80x9d shown in FIGS. 9 and 10, the O-ring 34 made of rubber and the restraint member 36 made of acetyl resin are provided between the outer circumferential face 10a of the holding plate 10 and the inner circumferential face 24a of the concave section 26 so as to limit the horizontal movement of the holding plate 10.
However, the O-ring 34 and the restraint member 36 allow the holding plate 10 in the concave section 26 to move in the radial directions. Therefore, in the abrasive machine shown in FIGS. 9 and 10, the gravity center of the wafer xe2x80x9cWxe2x80x9d is apt to shift from the rotational axis thereof while abrading the wafer xe2x80x9cWxe2x80x9d. If the gravity center of the wafer xe2x80x9cWxe2x80x9d is shifted from the rotational axis, the edge of the wafer xe2x80x9cWxe2x80x9d is diagonally abraded.
Further, the O-ring 34 and the restraint member 36 line- or plane-contact the outer circumferential face 10a of the holding plate 10 and the inner circumferential face 24a of the concave section 26 throughout the faces 10a and 24a, so the holding plate 10 cannot be smoothly projected from and retracted into the concave section 26 by friction there between.
A first object of the present invention is to provide a wafer abrasive machine, in which an elastic sheet member for suspending and biasing a holding plate toward an inner part of a concave section of a head member is reinforced by a cloth-formed reinforcing member capable of easily extending and in which a gravity center and a rotational axis of a wafer can be corresponded while abrading the wafer so as to smoothly move the holding plate, etc. in the concave section.
A second object of the present invention is to provide a wafer abrasive machine, which makes an abrasion cloth of an abrasive plate flat so as not to diagonally abrade an edge of the wafer.
To achieve the objects, the inventors of the present invention have studied and found that the gravity center and the rotational axis of the wafer, which is held by the holding plate and pressed onto an abrasive face of an abrasive plate, can be corresponded by providing spherical bodies between an outer circumferential face of the holding plate, which is suspended and biased upward by the elastic sheet member, and an inner circumferential face of the concave section of the head member. By corresponding the gravity center of the wafer to the rotational axis thereof, the holding plate can be smoothly projected from and retracted into the concave section of the head member.
Namely, a first structure of the present invention is the abrasive machine, in which a surface of a wafer held by a holding plate is pressed onto an abrasive face of an abrasive plate and relatively moved with respect thereto so as to abrade the surface of the wafer, comprises:
a head member including a concave section, in which the holding plate, whose wafer holding face is headed toward the abrasive face of the abrasive plate, is accommodated;
an elastic sheet member suspending the holding plate and biasing the holding plate toward an inner part of the concave section of the head member, the elastic sheet member being reinforced by a cloth-formed reinforcing member;
a space for storing pressure fluid which pushes the holding plate toward the abrasive plate against elasticity of the elastic sheet member, the space being formed between the elastic sheet member and an inner upper face of the concave section of the head member; and
a plurality of spherical bodies being provided between an outer circumferential face of the holding plate and an inner circumferential face of the concave section of the head member, the spherical bodies simultaneously point-contact the both circumferential faces.
And, the inventors also found that the second object can be achieved by biasing a dress ring, which encloses the holding plate and presses the abrasive face of the abrasive plate, by the elastic sheet member.
Namely, a second structure of the present invention is the abrasive machine, in which a surface of a wafer held by a holding plate is pressed onto an abrasive face of an abrasive plate and relatively moved with respect thereto so as to abrade the surface of the wafer, comprises:
a head member including a concave section, in which the holding plate, whose wafer holding face is headed toward the abrasive face of the abrasive plate, and a dress ring, which encloses the holding plate and presses the abrasive face of the abrasive plate so as to make it flat, are accommodated;
an elastic sheet member suspending the holding plate and the dress ring and biasing the both toward an inner part of the concave section of the head member, the elastic sheet member being reinforced by a cloth-formed reinforcing member;
a space for storing pressure fluid which pushes the holding plate toward the abrasive plate against elasticity of the elastic sheet member, the space being formed between the elastic sheet member and an inner upper face of the concave section of the head member; and
a plurality of spherical bodies being provided between an outer circumferential face of the holding plate and an inner circumferential face of the dress ring and between an outer circumferential face of the dress ring and an inner circumferential face of the concave section of the head member, the spherical bodies simultaneously point-contact the circumferential faces.
In the abrasive machine having the first structure, the elastic sheet member is reinforced by the cloth-formed reinforcing member, degree of extension of the elastic sheet can be in a proper range.
Since the spherical bodies simultaneously point-contact the outer circumferential face of the holding plate, which is suspended and biased by the elastic sheet member, and the inner circumferential face of the concave section of the head member, the spherical bodies can prohibit the movement of the holding plate, for example, a movement in the radial direction of the concave section, which is caused by the directional property of the extension of the elastic sheet member. Therefore, the gravity center and the rotational axis of the wafer can be corresponded during the abrasion, so that the wafer can be uniformly abraded and the diagonal abrasion of the edge of the wafer can be prevented.
Further, the spherical bodies, which simultaneously point-contact the outer circumferential face of the holding plate and the inner circumferential face of the concave section of the head member, make the holding plate smoothly project from and retract into the concave section of the head member.
In the abrasive machine having the second structure, the dress ring enclosing the holding plate is accommodated in the concave section together with the holding plate.
The holding plate and the dress ring are suspended and inwardly biased by the elastic sheet member. The dress ring presses the abrasive face along the edge of the wafer, which is pressed depressed by the wafer, so as to make it flat. By making the abrasive face flat, the diagonal abrasion of the edge of the wafer can be prevented.
The elastic sheet member is reinforced by the cloth-formed reinforcing member, degree of extension of the elastic sheet can be in a proper range. Since the spherical bodies simultaneously point-contact the outer circumferential face of the holding plate, which is suspended and biased by the elastic sheet member, and the inner circumferential face of the dress ring and between the outer circumferential face of the dress ring and the inner circumferential face of the concave section of the head member, the spherical bodies can prohibit the movement of the holding plate, etc., which is caused by the directional property of the extension of the elastic sheet member. Therefore, the gravity center and the rotational axis of the wafer can be corresponded during the abrasion, and the dress ring can make the abrasion face of the abrasive plate, so that the wafer can be highly uniformly abraded.
Further, the spherical bodies, which simultaneously point-contact the circumferential faces, make the holding plate smoothly project from and retract into the concave section of the head member.